Minor - removed unused pytest marker, explanation on using solargraph in readme

Also removed solargraph installation from CI

.github/workflows/pytest.yml

@@ -123,9 +123,7 @@ jobs:
           ruby-version: '3.4'
       - name: Install Ruby language server
         shell: bash
-        run: |
-          gem install solargraph
-          gem install ruby-lsp
+        run: gem install ruby-lsp
       - name: Install Zig
         uses: goto-bus-stop/setup-zig@v2
         with: