docs: add installation and configuration instruction for Emacs (#538)

* doc: add installation and configuration instruction for Emacs

* docs: refinement

* docs: help newbies a bit

---------

Co-authored-by: Myriad-Dreamin <camiyoru@gmail.com>

docs/tinymist/frontend/emacs.typ

@@ -0,0 +1,106 @@
+#import "/docs/tinymist/frontend/mod.typ": *
+
+#show: book-page.with(title: "Tinymist Emacs Extension")
+
+Run and configure tinymist in Emacs for Typst.
+
+== Features
+<features>
+See #link("https://github.com/Myriad-Dreamin/tinymist#features")[Tinymist Features] for a list of features.
+
+
+== Finding Executable
+<finding-executable>
+To enable LSP, you must install `tinymist`. You can find `tinymist` on:
+
+- Night versions available at #link("https://github.com/Myriad-Dreamin/tinymist/actions")[GitHub Actions];.
+- Stable versions available at #link("https://github.com/Myriad-Dreamin/tinymist/releases")[GitHub Releases];. \
+  If you are using the latest version of
+  #link("https://codeberg.org/meow_king/typst-ts-mode")[typst-ts-mode], then
+  you can use command `typst-ts-lsp-download-binary` to download the latest
+  stable binary of `tinymist` at `typst-ts-lsp-download-path`.
+
+
+You can also compile and install *latest* `tinymist` by #link("https://www.rust-lang.org/tools/install")[Cargo];.
+
+```bash
+cargo install --git https://github.com/Myriad-Dreamin/tinymist --locked tinymist
+```
+
+
+== Setup Server
+<setup-server>
+
+```el
+(with-eval-after-load 'eglot
+  (with-eval-after-load 'typst-ts-mode
+    (add-to-list 'eglot-server-programs
+                 `((typst-ts-mode) .
+                   ,(eglot-alternatives `(,typst-ts-lsp-download-path
+                                          "tinymist"
+                                          "typst-lsp"))))))
+```
+
+Above code adds `tinymist` downloaded by `typst-ts-lsp-download-binary`, `tinymist` in
+your PATH and `typst-lsp` in your `PATH` to the `typst-ts-mode` entry of `eglot-server-programs`.
+
+
+== Extra Settings
+<extra-settings>
+=== Configuring LSP Server
+<configuring-lsp-server>
+
+You can either use `eglot-workspace-configuration` or specifying launch
+arguments for `tinymist`.
+
+==== eglot-workspace-configuration
+<eglot-workspace-configuration>
+
+For example, if you want to export PDF on save:
+
+```el
+  (setq-default eglot-workspace-configuration
+                '(:exportPdf "onSave"))
+```
+
+Here is an example for both configuring `pylsp` and `tinymist`
+
+```el
+  (setq-default eglot-workspace-configuration
+                '(:pylsp (:plugins (:ruff (:enabled t)))
+                         :exportPdf "onSave"))
+```
+
+NOTE: Currently, `tinymist` doesn't support having its name as the top-level
+configuration entry, so the following configuration won't work:
+
+```el
+  (setq-default eglot-workspace-configuration
+                '(:pylsp (:plugins (:ruff (:enabled t)))
+                  :tinymist (:exportPdf "onSave")))
+```
+
+You can also have configuration per directory. Be sure to look at the
+documentation of `eglot-workspace-configuration` by #link("https://www.gnu.org/software/emacs/manual/html_node/emacs/Name-Help.html")[`describe-symbol`]..
+
+See #link("https://github.com/Myriad-Dreamin/tinymist/tree/main/editors/neovim/Configuration.md")[Tinymist Server Configuration]
+for references.
+
+
+==== Launch Arguments
+
+For example:
+
+```el
+(with-eval-after-load 'eglot
+  (with-eval-after-load 'typst-ts-mode
+    (add-to-list 'eglot-server-programs
+                 `((typst-ts-mode) .
+                   ,(eglot-alternatives `((,typst-ts-lsp-download-path "--font-path" "<your-font-path>")
+                                          ("tinymist" "--font-path" "<your-font-path>")
+                                          "typst-lsp"))))))
+```
+
+You can run command `tinymist help lsp` to view all available launch arguments for
+configuration.
+